Thermally assisted magnetic recording or heat-assisted magnetic recording (HAMR) generally refers to the concept of locally heating a recording medium to reduce the coercivity of the medium. Such reduced coercivity allows the applied magnetic writing fields to more easily direct the magnetization within the recording medium during the temporary magnetic softening caused by the heat source. HAMR allows for the use of small grain media, with a larger magnetic anisotropy at room temperature to assure sufficient thermal stability, which is desirable for recording at increased areal densities. HAMR can be applied to any type of magnetic storage media including tilted media, longitudinal media, perpendicular media, and patterned media. By heating the media, the Ku or coercivity is reduced such that the magnetic write field is sufficient to write to the media. Once the media cools to ambient temperature, the coercivity has a sufficiently high value to assure thermal stability of the recorded information.
In HAMR, information bits are recorded on a data storage medium at elevated temperatures, and the data bit dimension can be determined by the dimensions of the heated area in the storage medium or the dimensions of an area of the storage medium that is subjected to a magnetic field. In one approach, a beam of light is condensed to a small optical spot onto the storage medium to heat a portion of the medium and reduce the magnetic coercivity of the heated portion. One example of a recording head for use in HAMR generally includes a write pole and a return pole magnetically coupled to each other through a yoke or pedestal, and a waveguide for focusing light onto the storage medium. The waveguide is positioned between the write pole and the return pole. Light is coupled into the waveguide above the yoke and is transmitted through the waveguide on opposite sides of the yoke.